The present invention concerns a pipe fitting for connecting in a pipe line, in particular a metallic one, with a pipe union containing a receiving opening for the pipe line, a swivel nut, which can be threadedly connected with the pipe union, as well as a metallic cutting ring. The cutting ring is disposed between the pipe union and the swivel nut, where the cutting ring, with an outer cone, acts jointly with an inner cone of the pipe union in such a manner, that the cutting ring--over a certain region--is deformed toward the interior in a radial direction, when the swivel nut is tightened. The cutting ring cuts into the material of the pipe line with at least one cutting edge aided by a notch effect and under conditions of a form-fit, and where the cutting ring contains an essentially radial contact surface where it joins the outer cone for the purpose of generating a contact at a face surface of the pipe union in such a manner, that the tightening force is limited.
Such pipe fittings are sufficiently well known from several publications. Thus, for example, the DE 43 04 534 A1 describes such a "connection system", where only a metallic seal by means of two cutting edges, which cut into the pipe, is provided. The pamphlet deals primarily with the improvement of the mechanical support of the pipe line, for which the cutting ring is to consist of a fully hardened material or a material that is hardened throughout. Optionally, the cutting ring may, in this case, include a coating over at least a portion of its extent, which in particular may contain PTFE, and which coating reduces friction--and thus improves the sliding ability.
A similar pipe fitting is disclosed by the FR-A-2 568 665. In this case, a sealing ring--in addition to the metallic seal--is provided, which is positioned axially in front of the cutting ring in the gap between the pipe line and the interior cone of the pipe union. Here, under certain circumstances a "flowing away" of the sealing material, especially into the gap between the union and the pipe, can occur. This is, of course, detrimental to the sealing effect.
Something similar is described by the DE 44 26 445 C2. In addition, in the case of this well known pipe fitting, it is contemplated, that an open surface be provided between the outer cone of the cutting ring and its contact surface in such a manner, that when it is assembled, a free space is generated between the open surface and the interior cone of the union. By this means, radial stress concentrations at the front face of the pipe union are to be avoided.
In the DE 40 41 677 a pipe fitting is described, which is not of the same general type inasmuch as a so-called excessive assembly cannot be avoided by means of limiting the tightening force, because the cutting ring does not include a radial stop surface. However, several different embodiments of an additional seal arrangement with at least one circumferential seal made of an elastomeric material have already been described. In this case, primarily only the gap, which is located directly between the pipe line and the interior surface of the pipe union, is sealed. In some embodiments the seal is practically divided into two sealing elements, where either the cutting ring is sealed against the pipe line and the pipe union, or the swivel nut is sealed directly against the pipe union and the pipe line.
The present invention is now based on the task of improving a pipe fitting of this general type, especially with regard to its sealing capability.
According to the invention this has been achieved, in that the cutting ring includes an elastomeric circumferential seal in the transition region between the outer cone and the contact surface in such a manner, that, in the assembled condition, the circumferential seal, which is subjected to an elastic initial stress (in a chamber), is disposed between the cutting ring, on the one hand, and at least one partial region of the interior cone of the pipe union, which is adjacent the face surface, on the other hand.
In this case, it is especially advantageous, that a good retention of the circumferential seal can be ensured, so that a "flowing away" of sealing material can be largely avoided. To do this, it is advantageous if the circumferential seal is located in a circular groove of the cutting ring, which is formed between the outer cone and the contact surface. Preferably, the circular groove blends directly into the contact surface. By this it is meant, that the circular groove, which on its two axial sides is bounded by essentially radial flank surfaces, blends directly into the contact surface, so that this flank surface of the groove and the contact surface lie practically in a common plane.
Preferably, the circumferential seal is either located only in the cone region with a primarily radial sealing effect or, however, it is disposed in combination in the cone region as well as between the contact surface and the face surface of the pipe union with a radial as well as an axial sealing effect. In the latter case, the contact surface of the cutting ring is thus indirectly brought into contact with the face surface of the pipe union by way of a section of the circumferential seal.
In order to achieve an especially good and reliable seal even against high internal pressures of the system, it is advantageous, if the circular groove receiving the circumferential seal has a groove bottom, which, with regard to its diameter is at least in a certain region--smaller than the largest diameter at the face end of the interior cone of the pipe union in such a manner, that, in a chamber thus formed toward the interior cone, a circumferential seal can be housed, which has sufficiently large volume for a compression of the seal. This can, additionally, also be influenced by a certain design of the circumferential contour of the circular groove or the bottom of the groove, for which a few different embodiments will be described in greater detail below. By means of the contour of the circular groove, by the way, the deformation behavior of the cutting ring can be favorably influenced, when the fitting is tightened.
Further advantageous design characteristics of the invention are contained in the dependent claims as well as in the description below.
On the basis of several preferred examples of embodiments shown in the drawing, the invention shall be explained in greater detail below. The following is shown: